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3D Device Simulation Using ATLAS/DEVICE3D

New developments in ATLAS have led to the introduction
of three new 3D products under ATLAS: DEVICE3D, INTERCONNECT3D and
THERMAL3D. These products replace the standalone THUNDER program.
The new DEVICE3D product within ATLAS extends the capabilities of
S-PISCES in modeling general non-planar 3D structures. The structural
definition, models, material parameters and solution techniques
are extensions to the 2D SPISCES syntax. DEVICE3D is integrated
into the VWF allowing RSM's of 3D effects to be generated. An example
of this is shown in Figure 1.

A completely new graphics program, TONYPLOT3D,
is also being released. This program includes standard graphics
libraries to take full advantage of graphics accelerators.

3D Structure Generation

DEVICE3D supports structures defined on 3D prismatic
meshes. Structures may have arbitrary geometries in two dimensions
and consist of multiple slices in the third dimension. There are
two methods for creating a 3D structure that can be used with DEVICE3D.
One is through the command syntax of ATLAS and the other through
an interface to the structure definition and meshing program, DEVEDIT3D.
DEVEDIT3D provides the ability to read in 2D structures from ATHENA
and extend them non-uniformly to create 3D structures for DEVICE3D.

Narrow Width Effects in MOSFETs

DEVICE3D can simulate narrow width effects using
structures defined in DEVEDIT3D. Potentially, a 2D cross section
of field oxide bird's beak from ATHENA can be used as the input
to DEVEDIT3D to provide accurate doping and geometry. Variation
in the width of the device and doping under the field oxide can
be defined as experimental variables in VWF. The combination of
DEVEDIT3D and DEVICE3D running under the VWF is able to produce
results for threshold voltage and other device parameters. Figure
1 illustrates the threshold voltage increase with decreasing device
width and increasing field doping.

Figure 1. NMOS threshold voltage
as a junction of device width and field implant.

Single Event Upset

A model for electron/hole generation by ionizing
radiation is included in DEVICE3D. Users can specify entry and exit
coordinates for an ion track through the device. The generation
rate can vary with length along the track, distance from the track
and time. Figure 2 shows the electron concentration after an angled
alpha particle strike through a pn junction. DEVICE3D is able to
simulate the transient current generated from the particle strike.

DEVICE3D includes features necessary for simulation
of Flash EEPROM programming and erasing. Both hot electron injection
and Fowler Nordheim tunneling models are available in DEVICE3D.
Charge boundary conditions for floating gates can also be defined.
A band-to-band tunneling model is included for use in erasing simulations.
Figure 3 shows the electron current density in a 3D EEPROM device
during programming.

Figure 3. Current density at
the silicon surface of a 3D EEPROM structure.